1. Field of the Invention
The present invention relates to fluid pressure control valves adapted for use in motor vehicle braking systems, and particularly, but not exclusively, to a fluid pressure control valve incorporated with dual hydraulic braking circuits connecting a tandem master cylinder to the left and right rear-wheel brake cylinders to independently modulate the hydraulic pressure applied to the rear-wheel brake cylinders from the master cylinder during braking.
2. Description of the Prior Art
In Japanese Patent Early Publication No. 54-147372, there has been proposed a fluid pressure control valve which includes first and second proportioning valves arranged in parallel with each other and disposed respectively within dual hydraulic braking circuits connecting a tandem master cylinder to the left and right rear-wheel brake cylinders. In the control valve, respective control plungers for the proportioning valves are received by a spring receiver and loaded by a single compression coil spring interposed between the spring receiver and a single control piston which is axially movable in response to fluid pressure applied thereto from one of the braking circuits through an inertia-controlled valve. In such an arrangement of the control valve, the spring receiver is provided as an equalizer for the control plungers. It is, therefore, apparent that if the center of the coil spring acting on the spring receiver is radially displaced towards one of the control plungers due to errors in manufacture and assembly of the spring receiver and the coil spring, the bias on one of the control plungers will differ from the bias on the other control plunger. This results in a difference in function between the proportioning valves and causes undesired problems during braking.
The control valve is further provided with a changeover valve which is arranged to apply fluid pressure from the other braking circuit to the inertia-controlled valve in the occurrence of damage of the one of the braking circuits. Such an arrangement of the changeover valve results in an increase of the manufacturing cost and size of the control valve and results in a complicated arrangement of the conduits for the control valve.